Synthesis, Structures, and CO Release Capacity of a Family of Water-Soluble PhotoCORMs: Assessment of the Biocompatibility and Their Phototoxicity toward Human Breast Cancer Cells

Two
manganese­(I) carbonyl complexes derived from 2-(pyridyl)­benzothiazole
(pbt) and 1,10-phenanthroline (phen) release carbon monoxide (CO)
under low-power broad-band visible-light illumination. CO photorelease from [Mn­(CO)3(pbt)­(PTA)]­CF3SO3 (1, where PTA = 1,3,5-triaza-7-phosphaadamantane)
is accompanied by an emergence of a strong fluorescence around 400
nm from almost nonfluorescent preirradiated 1. However,
[Mn­(CO)3(phen)­(PTA)]­CF3SO3 (2) showed no such phenomenon upon prolonged illumination under
similar experimental conditions. The two analogous rhenium­(I) complexes,
namely, [Re­(CO)3(pbt)­(PTA)]­CF3SO3 (3) and [Re­(CO)3(phen)­(PTA)]­CF3SO3 (4), have also been synthesized and characterized
to compare their photo properties with the manganese congeners. Complexes 3 and 4 exhibit moderate CO release upon irradiation
with low-power UV light. All four complexes are highly
soluble in anaerobic/aerobic aqueous media and are also considerably
more stable when kept under dark conditions. The inherently luminescent
rhenium complex 3 was utilized to demonstrate cellular
internalization of these types of compounds by MDA-MB-231 (human breast
cancer) cells, while the two biocompatible manganese­(I) complexes
(1 and 2) have been applied to assess the
cell viability of these malignant cells upon CO delivery.